Definition, Principle, Functions, and Examples of Anticodon

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Definition, Principle, Functions, and Examples of Anticodon

Table of Content

What is Anticodon?

Anticodon Principle

Anticodon Functions

Anticodon Examples

What is Anticodon?

An anticodon is a trinucleotide sequence found on one arm of tRNA (transfer RNA) that is complementary to the mRNA sequence or codon (messenger RNA).

• The anticodon sequence is found on the anticodon loop of the tRNA and is important in the translation process.
• The amino acid attaches to the tRNA's 3' adenosine end, resulting in an aminoacyl tRNA.

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Anticodon Principle

• mRNA and tRNA are antiparallel in their organisation.
• To begin translation, the first base of the codon on mRNA (5' to 3') connects with the third base of the anticodon on tRNA.

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FIGURE shows pairing relationship of codon and anticodon. (a) Alignment of two RNAs is anti parallel. The tRNA is shown in the traditional cloverleaf configuration. (b) Three different codon pairing relationships are possible when the tRNA anticodon contains inosinate.

• Each tRNA contains a unique amino acid and binds to the complementary mRNA codon on the 30s subunit in prokaryotes and the 40s subunit in eukaryotes.
• The initial anticodon is accepted by the A site during this process, and it then attaches to the P site on mRNA, where the protein's developing polypeptide is kept together.
• The anticodon travels three nucleotides farther to the E site when the amino acid carried by the tRNA is transferred (Exit).
• If complete paring between codon and anticodon is assumed, then each amino acid will require its own tRNA.
• This, however, is not the case. Some tRNAs include the nucleotide Inosinate (I), which contains the rare base 'hypoxanthine.'

• This inosinate has the ability to establish hydrogen bonds with three distinct nucleotides: U, C, and A.
• Inosinate binds to these nucleotides through weaker hydrogen bonds, resulting in weaker pairings than typical nucleotide pairings.
• Because certain tRNAs have this unique nucleotide, roughly 32 tRNAs can code for 61 amino acids.
• The Wobble theory describes the imperfect pairing of inosinate with other nucleotides, in which there is perfect pairing between two nucleotides but faulty or weak pairing between the third nucleotide.

Anticodon Functions

• An anticodon is in charge of the translation process that results in the formation of a protein polypeptide.
• The amino acid specificity is determined by an anticodon.
• Anticodon is in charge of starting and stopping the translation process.
• In prokaryotes and eukaryotes, the first anticodon is UAC, which binds to the mRNA sequence AUG.
• The tRNA's initiator anticodon binds to a corresponding codon on mRNA, adding the first amino acid to the protein polypeptide. In prokaryotes, the first amino acid is N-formyl-methionine, but in eukaryotes, the first amino acid is unmodified methionine.
• Because the tRNA anticodon is in charge of initiating translation, it is also in charge of terminating translation.
• When the anticodon on tRNA is – AUU, AUC, or ACU, one of these three sequences ends.

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Anticodon Examples

The following anticodons are feasible based on the genetic code with codons that code for amino acids:

• The anticodons for amino acid Phenylalanine are – AAA, AAG
• The anticodons for amino acid Leucine are – AAU, AAC, GAA, GAG, GAU, GAC
• The anticodons for amino acid Isoleucine are – UAA, UAG, UAU
• The anticodon for amino acid Methionine is – UAC
• The anticodons for amino acid Valine are – CAA, CAG, CAU, CAC
• The anticodons for amino acid Serine are – AGA, AGG, AGU, AGC, UCA, UCG
• The anticodons for amino acid Proline are – GGA, GGG, GGU, GGC 
• The anticodons for amino acid Threonine are –  UGA, UGG, UGU, UGC 
• The anticodons for amino acid Alanine are – CGA, CGG, CGU, CGC 
• The anticodons for amino acid Tyrosine – AUA, AUG 
• The anticodons for amino acid Histidine are – GUA, GUG 
• The anticodons for amino acid Glutamine are – GUU, GUC 
• The anticodons for amino acid Asparagine are –  UUA, UUG 
• The anticodons for amino acid Lysine are – UUU,UUC 
• The anticodons for amino acid aspartic acid are – CUA, CUG
• The anticodons for amino acid Glutamine acid are –  CUU, CUC
• The anticodons for amino acid Cysteine are- ACA, ACG
• The anticodons for amino acid Tryptophan are – AGU, ACC
• The anticodons for amino acid Arginine are – GCA, GCG, GCU, GCC, UCU, UCC
• The anticodons for amino acid Glycine are – CCA, CCG, CCU, CCC